Tight! Nice and crisp controls and graphics. Feels super finished already! Depositing the shapes to the upgrade-system and then going to the computer to buy shit felt super good. The actual upgrades themselves unfortunately felt lacking. Just increasing my HP- or DMG-stat by couple of points didn't feel that rewarding.
There was also a visual bug for me; Whenever I alt-tab'd away from the game and back, the background and the walls had changed colors to bright basic colors. Like the whole floor was a flat, saturated green and walls red or something along those lines. It fixed itself though whenever I alt-tab'd away and back a second time.
All in all, completed the game, enjoyed myself. Would have liked a little more challenge, now I was never in a near-death scenario because the upgrades pumped up my HP a lot and I could keep the enemies at bay with the weapon. I say it's a good prototype. With some more variety in enemies, player upgrades and levels would be a great one!